The field of the invention pertains to structural blocks such as those commonly referred to as "concrete blocks" used for constructing both load bearing and non-load bearing walls of buildings. Such blocks are usually formed with two or three vertical holes formed therein and made of concrete or cinders with a cement mortar as a binder. Less commonly the blocks may be constructed of fired brick or clay tile.
The holes in the blocks provide a substantial decrease in weight and material without a commensurate decrease in structural strength. The holes also provide some insulating value as closed airspace in a completed wall. More recently semi-cylindrical inserts formed of rigid foam are being inserted into the holes of conventionally manufactured blocks after the blocks are molded and cured or fired. The inserts partially fill the holes in the blocks. Such inserts, however, do not decrease the thermal conduction through the interior webs joining the exterior and interior faces of the blocks together. Other approaches include filling of the holes with foam or other insulating material to decrease the heat transfer effect of thermal convection within the holes or the construction of walls with parallel rows of blocks separated by a layer of insulation.